An atomic layer deposition (ALD) process is a well known deposition technique in the semiconductor industry. The ALD process employs a precursor material which can react with or chemisorb on a surface in process to build up successively deposited layers, each of which layers being characterized with thickness about only one atomic layer. Subject to properly selected process conditions, the chemisorption reaction has a self-limiting characteristic, meaning that the amount of precursor material deposited in every reaction cycle is constant and the precursor material is restricted to growing on the surface, and therefore the film thickness can be easily and precisely controlled by the number of the applied growth cycles.
Conventionally, a batch of ALD process usually consists of multiple ALD reaction cycles, each of which ALD reaction cycles involves consequently performing steps of introducing a first gaseous precursor pulse to a surface in process, pulsing an inert gas to purge or evacuate the excess gaseous precursor after the surface is saturated with an atomic layer of the first gaseous precursor, pulsing a second gaseous precursor and purging by an inert gas pulse or evacuating. A single ALD reaction cycle is continuously repeated until a target thickness for the deposited atomic layer on the surface in process is achieved.
The conventional ALD process is widely applicable for growing a thin film, such as a high-k dielectric layer, a diffusion barrier layer, a seed layer, a sidewall, a sidewall oxide, a sidewall spacer for a gate, a metal interconnect and a metal liner etc., in a semiconductor electronic element.
Often, the conventional ALD process is implemented in a furnace, and one batch of ALD process can only form one scale of thickness for an ALD layer on a substrate or a wafer in the furnace. However, for example, there usually exist five different thicknesses in a range from 20A, 25A, 30A, 40A to 43A needed to be formed for sidewall oxidations in one semiconductor device.
Thus, there arises a difficulty to reach full batch control, for example one hundred and twenty-five pieces, since a sidewall stage would require four hours of quality check time for defect reduction. The factors stated above lead to a limitation on the efficiency of ALD for wafer capacity utilization currently, while the quantity of the same thickness of wafer in process (WIP) would be lower than fifty pieces in comparison with the full batch load. This will cause unsatisfactory tool efficiency, and a corresponding low WIP performance will degrade the tool efficiency as well.
However, the ALD process for the batch load with respect to currently uniform size injectors located within the chamber is not yet good enough to be satisfactory, failing to overcome a series of issues related to handling different layer deposition thicknesses for different wafers of the load batch when different reaction cycles are used to elevate the capacity utilization of the batch load within the chamber vacuum furnace.
In addition, full batch control, which includes one hundred and twenty five wafers in process, is difficult due to the sidewall oxidation stage requiring four hours of Q-time (quality time) for defect reduction. Currently, only fifty pieces having same wafer thickness can be in process, which causes poor tool efficiency as well.
There is a need to solve the above deficiencies/issues.